Simplify the following expression: $q = \dfrac{1}{6r} + \dfrac{1}{4r}$
Answer: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $6r$ and $4r$ $\lcm(6r, 4r) = 12r$ $ q = \dfrac{2}{2} \cdot \dfrac{1}{6r} + \dfrac{3}{3} \cdot \dfrac{1}{4r} $ $q = \dfrac{2}{12r} + \dfrac{3}{12r}$ $q = \dfrac{2 +3}{12r}$ $q = \dfrac{5}{12r}$